Biorobotic approaches to the study of motor systems

Biorobotics is a promising new area of research at the interface between biology and robotics. Robots can either be used as physical models of biological systems or be directly inspired by biological studies. A great deal of progress has recently been made in biorobotic studies of locomotion, orientation, and vertebrate arm control.     

Clinical trials and tribulations: lessons learned from recruiting pregnant ex-smokers for relapse prevention.

The development of smoking cessation and relapse prevention interventions for pregnant and postpartum women is a public health priority. However, researchers have consistently reported substantial difficulty in recruiting this population into clinical trials. The problem is particularly acute for relapse prevention studies, which must recruit women who have already quit smoking because of their pregnancy. Although these individuals are an important target for tobacco control efforts, they represent an extremely small subgroup of the general population. This paper describes multiple recruitment strategies used for a clinical trial of a self-help relapse prevention program for pregnant women. The effectiveness of the strategies and the direct expense per participant recruited are provided. A proactive recruitment strategy (telephoning women whose phone numbers were purchased from a marketing firm) was ultimately much more successful than a variety of reactive strategies (advertisements, press releases, direct mail, Web placement, health care provider outreach). We found few differences between proactively and reactively recruited participants on baseline variables. The primary difference was that the former had smoked fewer cigarettes per day and reported lower nicotine dependence prior to quitting. Strengths and limitations of the recruitment strategies are discussed.     

The effects of surface-active materials on the oscillations of a liquid jet

The oscillatory motion and stability of a liquid jet are examined in the context of a theory which accounts for local variations of interfacial tension induced by expansion and contraction of an interface containing adsorbed molecules. The presence of a soluble surfactant alters the oscillation frequency as well as growth and decay rates via damping in a boundary layer. It is found that the frequency alteration is a substantial effect when considered in the context of measurements made with oscillating jets, i.e. the dynamic surface tension. When viscous effects are large the presence of surfactant may introduce oscillatory character in place of the aperiodic temporal behavior of pure liquids.     

Great Lakes Beginning-of-Month Water Levels and Monthly Rates of Change of Storage

Time series of beginning-of-month water levels and rates of change of lake storage were determined for each of the Great Lakes and Lake St. Clair for 1941-1975 period. The Thiessen polygon procedure was used to compute the beginning-of-month levels because it provides more representative over-all lake levels than straight averaging and requires minimum subjectivity. The effect of crustal movement on the rate of change of lake storage was investigated and found to be negligible. A gage density analysis showed good agreement between various size gage networks with the maximum deviation between networks decreasing with increasing gage density. Thiessen polygon weighting factors are presented for the current gage networks to enable future extension of the time series.     

Relative Accuracy of Connecting Channel Discharge Data with Application to Great Lakes Studies

The flows in the Great Lakes connecting channels are a major component in the water balance of the Great Lakes Basin. The increased emphasis on Great Lakes water quality and quantity requires an assessment of the accuracy of both measured and computed connecting channel discharge data. In this study, the standard error of typical discharge measurements was found to be approximately 3 to 5 percent, depending upon the number of panels used in the cross section. Mesurement sets were found to have a practical limit of about 25 measurements. The standard error of a set of measurements was found to be on the order of 1 percent. The procedure used to compute the published flows of the Niagara River was found to have an apparent bias of about 2 percent on the high side. It is recommended that the published Niagara River flows be adjusted prior to use in detailed water balance studies.     

Molecular genetic analysis of plastocyanin biosynthesis in Chlamydomonas reinhardtii

Five plastocyanin-deficient mutants were identified from a population of UV-mutagenized Chlamydomonas reinhardtii cells. Genetic complementation experiments indicated that four mutants represented alleles at the PCY1 locus (pcy1-2, pcy1-3, pcy1-4, and pcy1-5). Sequence analysis confirmed that two strains, pcy1-2 and pcy1-3, carry a frameshift (-1) and a nonsense mutation, respectively, while strains pcy1-4 and pcy1-5 synthesize an extended protein as a result of read-through mutations at the stop codon. The C-terminal extension does not affect synthesis or processing of the pre-proteins, but the polypeptides are rapidly degraded after the second (lumenal) processing event. The frameshift mutation in pcy1-2 results in loss of Pcy1 mRNA, as noted previously for strain ac208 (pcy1-1), but the abundance of Pcy1 mRNA in strain pcy1-3, which carries a nonsense mutation at codon 26, is unaffected relative to wild-type cells. The decreased abundance of frameshifted Pcy1 mRNA is attributed to increased degradation rather than decreased synthesis, since the mRNAs can be stabilized by treatment of cells with cycloheximide or anisomycin. The fifth strain has a wild-type plastocyanin-encoding gene, but the strain accumulates apoplastocyanin at the expense of holoplastocyanin. We suggest that the mutation identifies a new locus (PCY2) whose function is required for normal holoplastocyanin accumulation. Like ac208 (pcy1-1), several of the new mutants were suppressed spontaneously owing to accumulation of cytochrome c6 (a functional substitute for plastocyanin). The suppressor mutation(s) displayed Mendelian inheritance and segregated independently from the PCY1 locus, which confirms that regulation of Cyc6 expression is not tightly linked to plastocyanin function.